When two objects are moving relative to each other, the range between the objects will achieve its global minimum range value at the closest point of approach (CPA) at the time of closest point of approach (TCPA). In sense and avoid applications, one object, such as an aircraft or other sensor platform, may be receiving measurements about the position and movement of another object or “target.” The target may be another aircraft or an airborne projectile or obstacle to be avoided, and the measurements may be range, Doppler, and angle measurements such as those typically generated by radar. These target measurements can be used to estimate CPA and TCPA.
Estimating these parameters involves prediction into the future. Measurement errors are amplified by the prediction process and thus dilute the accuracy of CPA and TCPA estimates. The measured data typically used for this prediction process is either extracted from the target position measurement or from the measured or derived Doppler data. While the position estimation process allows extrapolation of future positions, it is usually less accurate than the Doppler data when used to estimate either CPA or TCPA. However, the more accurate Doppler data does not provide a simple solution for the CPA and TCPA estimates, and it is adversely affected by the target and sensor platform accelerations. Accordingly, there remains a need for an improved technique for estimating CPA and TCPA from target measurements.